1. Field of the Invention
The present invention relates to a laminated heat exchanger used in the cooling cycle or the like in an air conditioning system for vehicles. The heat exchanger is constituted by laminating tube elements and fins alternately over a plurality of levels and in particular, the present invention relates to a laminated heat exchanger that adopts a structure in which a pair of tank portions are formed at one side of the tube elements and intake/outlet portions for heat exchanging medium are provided at one end in the direction of lamination or at the end surface of the core main body in the direction of the air flow.
2. Description of the Related Art
In order to respond to the demand for miniaturization of heat exchangers and to improve heat exchanging efficiency, applicant has developed the heat exchanger shown in FIGS. 1 and 2, and has conducted much research related to this heat exchanger. In this laminated heat exchanger, a core main body is formed by laminating tube elements alternately with fins 2 over a plurality of levels, a pair of tank portions 12, provided at one side of each tube element, are made to communicate via a U-shaped passage portion 13. A heat exchanging medium flow passage with a plurality of passes is formed in the core main body by providing communication between the tank portions 12 of adjacent tube elements as necessary. Also, intake/outlet portions (intake portion 4 and outlet portion 5) for the heat exchanging medium are provided at one end of the core main body in the direction of the lamination with one of these intake/outlet portions (intake portion 4) being made to communicate with a tank block 21, which constitutes one end of the heat exchanging medium flow passage, through a communicating pipe 30. The other of the intake/outlet portions (outlet portion 5) is made to communicate directly with a tank block 22, which constitutes the other end of the heat exchanging medium flow passage.
The applicant has also conducted various types of research into the one-side tank type laminated heat exchanger that is known in the prior art, as well as the heat exchanger described above. For instance, FIGS. 10 and 11A-B show one such heat exchanger. In this heat exchanger, a core main body is formed by laminating tube elements alternately with fins 2 over a plurality of levels, a pair of tank portions 12, provided at one side of each tube element (toward the bottom in the figures) are made to communicate via a U-shaped passage portion 13 and the tank portions 12 in adjacent tube elements are made to communicate as necessary to form a heat exchanging medium flow passage with a plurality of passes in the core main body. In these aspects, this heat exchanger is similar to the one described earlier. However, this heat exchanger is provided with intake/outlet portions (intake portion 4, outlet portion 5) for heat exchanging medium at the end surface of the core main body in the direction of the air flow.
In these heat exchangers described above, when the heat exchanging medium flows in through one of the intake/outlet portions (intake portion 4), the heat exchanging medium enters the tank block 21 which constitutes one end of the heat exchanging medium flow passage either directly or via the communicating pipe 30. After traveling through a plurality of passes, the heat exchanging medium reaches the tank block 22, which constitutes the other end of the heat exchanging medium flow passage, and it flows out through the other of the intake/outlet portions (outlet portion 5), which communicates with the tank block 22. In this process, the flow of the heat exchanging medium, in which it travels upward or downward through the U-shaped passage portions 13 of the tube elements, is counted as one pass and, for instance, a heat exchanger in which the heat exchanging medium passes through the U-shaped passage portions 13 twice, starting from the tank block constituting one end of the heat exchanging medium flow passage until it reaches the tank block constituting the other end, is referred to as a 4-pass heat exchanger and if it passes through the U-shaped passage portions three times, it is referred to as a 6-pass heat exchanger.
However, in the first type of heat exchanger, i.e., in a 4-pass cooling heat exchanger, in which the heat exchanging medium passes through a tank group without a partitioning portion 18 when it moves from the second pass to the third pass, as shown in FIG. 9A, the coolant tends to flow in the direction that runs at a right angle to the air flow in the structure described above, in which the coolant flows out from one end of the core main body. This results in the coolant collecting in the tube elements close to the outlet (one end in the direction of the lamination). In other words, in the area extending from the third pass through the fourth pass, the coolant does not readily flow toward the side close to the partitioning portion 18 and this has been proved true through testing. The test results are indicated by the broken lines in FIGS. 7 and 8A-B, which demonstrate that the tube temperature and the passing air temperature in the area of the partitioning portion close to the outlet are higher than those in the other areas.
In this context, the tube temperature (TUBU TEMP.) refers to the temperature of the tube element itself and the tube numbers (TUBU No.) in FIGS. 7 and 12 refer to the tube element numbers assigned starting from the left side in FIGS. 1 and 10. Also, the passing air temperature (AIR TEMP.) refers to the temperature of the air that has passed through the area between the tube elements and for which heat exchange has been performed with the fins. The air temperature was measured at a position that is away from the end surface of the core main body on the downstream side by 1.about.2 cm.
In a 6-pass heat exchanger, the heat exchanging medium flow also concentrates in the area toward the outlet side, away from the partitioning portion 18, as shown in FIG. 9B. As a result, it is assumed that the tube temperature and the passing air temperature in the area of the partitioning portion near the outlet will be different from those in the other areas.
Furthermore, in the latter type of heat exchanger, i.e., a 4-pass cooling heat exchanger, when the flow speed increases with the coolant flow rate per unit time increasing, the coolant will concentrate toward the end in the direction of the lamination when it moves from the second pass through the third pass, as shown in FIG. 14. Also, the coolant will not readily flow in the area toward the partitioning portion 18 in the area extending from the third pass through the fourth pass. The coolant is clearly demonstrated to flow in this manner by the test results indicated with the broken lines in FIG. 12, which show that the passing air temperature is higher in the area near the partitioning portion 18 compared to the other areas.